<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            box-sizing: border-box;
        }
        div{
            width: 100px;
            height: 100px;
            background-color: red;
         padding: 40px;
            /* border: 1px solid #000; */
            /* 
            1.solid 实线
            2.dashed 虚线
             */
             /* border-top: 10px solid #fff;
             border-right: 10px solid #fff;
             border-bottom: 10px solid green;
             border-left: 10px solid green; */
border-radius: 25px;

        }
    </style>
</head>
<body>
    <div>div</div>

</body>
</html>